You weren't behind moutain (a small hill, actually), 3/4 of your mech was exposed to 270 degrees of target arc, active radar. You were damaged, basically alone, far from base, and no AA support w/ at least two S/KN dedicated (whole match) flyers.
You could have taken any mech you wanted, but @ 1500m range, you get the same result. Consider it a blessing you got over 9 shots on target < 900m vs that Shiva B.
My opinions on the matter are known; but, this isn't any different than having an "oh shit" moment vs LT, except you got to shoot.
No offense, but the answer is obvious and these "why did I die" posts don't move the already well-posted ASF debate forward. Everyone dies in situations that are, or become, tactically untenable.
I think I should win like 90% of my fights, unfortunately reality, the server, the interwebs, other players, the alignment of the planets, my aging neurons, and good ole chance figure it otherwise.